WŁODZIMIERZ Grygiel and Alfred Grelowski
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: seawater temperature, salinity, oxygen content, upper and bottom water layers, autumn 2002, winter-spring 2003, southern Baltic.

Abstract.
The main hydrological parameters - seawater temperature, salinity, oxygen content - measured during four research surveys, conducted in October-November 2002 and February -March 2003 aboard the r/v BALTICA in the Polish EEZ, constitute the research materials analyzed by the authors. The basic aim of this article is to evaluate recent changes in the hydrological conditions of southern Baltic waters. The significant changes observed in water temperature and salinity between October 2002 and spring 2003 may have an impact on the effectiveness of cod spawning in 2003. In February 2003 a relatively heavy inflow of water with a salinity of 19.2 PSU was registered in the Bornholm Deep. The current inflow is regarded as cold as the water temperature in the near-bottom layer in the Bornholm Deep was 3.44^oC lower than the long-term February mean (1950-2002). Recent observations indicate that the inflow waters are continuing to spread to the eastern parts of the southern Baltic.